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De ideale hechtlaag voor elektronische chips

The Prefect Tie Coat for Electronic Packages

Problem description:

The Ultra-thin chip package (UTCP) is an extremely thin (< 100 µm) packaging technology for electronic chips, making it possible to realize fully flexible electronic systems. The thinned chips (down to 30 µm thickness) are embedded in a polyimide layer. The contacts to the chip are realized by making openings in the polyimide and metalizing these vias with copper. The copper is deposited by sputtering. To obtain a good adhesion between the copper and the polyimide, a thin metal layer is deposited in between, which is commonly known as "tie coat" layer.

A conceptual drawing of a UTCP package

Reactive magnetron sputtering is a deposition technique for forming thin layers. The layer thickness can vary from a few nanometer to several micrometers. This technique is applied on a large scale for depositing infrared reflecting multilayers on glass windows. It is based on magnetically assisted gas discharge. The ions, created in a plasma, bombard the cathode or target and knock off atoms from this target. These sputtered atoms propagate towards the substrate and form a layer. Reactive magnetron sputtering makes it possible to deposit several different metals and compositions.

Goal:

The tie coat layer is an important part of the UTCP technology. The master thesis is part of an investigation to improve the adhesion of copper on polyimide. Different materials (Cr, Ti, W and alloys) will be investigated. Next to the material choice, the deposition parameters also have a strong influence on the adhesion. By depositing the tie coat under specific condictions, the grain size, microstructure, and the texture of the layers can be varied. The deposited layers will be characterized by X-ray diffraction (XRD) and electron microscopy (SEM). A correlation with the quality of the tie coat will be investigated. Subsequent adhesion tests are performed at the Centre for Microsystems Technology (CMST).

The low thickness makes it possible to bend the UTCP in all directions

The goal of this master thesis is the research of the optimal compostion and deposition parameters for the tie coat. Both the characterization of the deposition parameters and the properties of the thin layers will be investigated.

We are looking for an enthusiastic student with an affinity for experimental work. Interest in collaboration with several reserrach groups is a plus. We present, next to a dedicated desk, a pleasant research envireonment to work together with different researchers.